Little problem with arm movement in my character's walk cycle
Your arm IK control bones (Arm.L and Arm.R) are positioned too far in parts of animation, so the arms need to extend too much and are no longer bent in elbow. That causes the elbow popping in the walk cycle.

Also the same bones are not looped, so that causes another discontinuity when looping the animation.

Keyframe these bones more carefully to not overextend the arms and loop them and the animation will be fine.